Mac: If there's one problem with cloud storage, it's that you actually have to remember to save your files to it. Quicksand is an app that automatically saves every file you open to your cloud storage drive so you don't have to remember.

Every time you open a file, Quicksand saves it to the cloud storage of your choice. You can also set it up so certain large files don't get synced, only certain file types are saved, or to keep the number of files uploaded below a certain number. Once you start using Quicksand you'll forget it's even there, but it's incredibly handy when you need it.